In “Cod genome reveals unusual immune system” (Nature News, August 10, 201 ) George Wigmore reports “Missing molecules show evolutionary flexibility, and may help fish farmers”:
It’s been known for many years that cod were more susceptible to certain illnesses, and the impaired MHC class II was system has been suggested as the reason, but how the cod managed to survive in considerable numbers was a mystery:
They lost the genes for “three important components of the adaptive immune system.”
One missing component is called the major histocompatibility complex (MHC) II, which presents fragments of bacteria and other pathogens to cells in the immune system to trigger a wider response. Cod also lack the gene for the proteins CD4, which interacts with MHC II, and invariant chain, which is involved in making and transporting MHC II.
However,
One way that cod compensate for their missing MHC II is by having ten times more genes than other vertebrates, including related fish species and humans, for another component of the immune system, called MHC I. MHC I takes proteins from within the cell, and displays them on the cell surface. If the immune system detects any foreign bodies, such as viral proteins, it destroys the infected cell.
This find may help produce better vaccines for cod, but that’s a stretch because most vaccines are developed to assist the missing MNC II system.
The finding could also challenge our understanding of the evolution and flexibility of the vertebrate immune system.
Well, if this is an example of “evolution in action,” it’s an example of successfully (for the most part) compensating for a loss, not of the development of new traits. Don;’t count on the pop science press to notice the distinction.
See also: You should have had more faith in cod.